The present invention relates to sand screens for use in the production of hydrocarbons from wells, and specifically to an improved sand screen having integrated sensors for determining downhole conditions and actuators for modifying the sand placement efficiency or controlling the production profile during the life of the reservoir.
Many reservoirs comprised of relatively young sediments are so poorly consolidated that sand will be produced along with the reservoir fluids. Sand production leads to numerous production problems, including erosion of downhole tubulars; erosion of valves, fittings, and surface flow lines; the wellbore filling up with sand; collapsed casing because of the lack of formation support; and clogging of surface processing equipment. Even if sand production can be tolerated, disposal of the produced sand is a problem, particularly at offshore fields. Thus, a means to eliminate sand production without greatly limiting production rates is desirable. Sand production is controlled by using gravel pack completions, slotted liner completions, or sand consolidation treatments, with gravel pack completions being by far the most common approach.
In a gravel pack completion, sand that is larger than the average formation sand grain size is placed between the formation and screen or slotted liner. The gravel pack sand (referred to as gravel, though it is actually sand in grain size), should hinder the migration of formation sand. FIG. 1 illustrates an inside-casing gravel pack 10. A cased hole 8 penetrates through a production formation 6 that is enveloped by non-producing formations 2. The formation 6 has been perforated 4 to increase the flow of fluids into the production tubing 14. If formation 6 is poorly consolidated, then sand from the formation 6 will also flow into the production tubing 14 along with any reservoir fluids. A gravel pack 12 can be used to minimize the migration of sand into the tubing. A successful gravel pack 12 must retain the formation sand and offer the least possible resistance to flow through the gravel itself.
For a successful gravel pack completion, gravel must be adjacent to the formation without having mixed with formation sand, and the annular space between the screen and the casing or formation must be completely filled with gravel. Special equipment and procedures have been developed over the years to accomplish good gravel placement. Water or other low-viscosity fluids were first used as transporting fluids in gravel pack operations. Because these fluids could not suspend the sand, low sand concentrations and high velocities were needed. Now, viscosified fluids, most commonly, solutions of hydroxyethylcellulose (HEC), are used so that high concentrations of sand can be transported without settling.
Referring to FIGS. 2a and 2b, the gravel-laden fluid can be pumped down the tubing casing annulus, after which the carrier fluid passes through the sand screen and flows back up the tubing. This is the reverse-circulation method depicted in FIG. 2a. The gravel is blocked by a slotted line or wire wrapped screen 16 while the transport fluid passes through and returns to the surface through the tubing 18. A primary disadvantage of this method is the possibility of rust, pipe dope, or other debris being swept out of the annulus and mixed with the gravel, damaging the pack permeability. Alternatively a crossover method is used, in which the gravel-laden fluid is pumped down the tubing 18, crosses over the screen-hole annulus, flows into a wash pipe 20 inside the screen, leaving the gravel in the annulus, and then flows up the casing-tubing annulus to the surface, as shown in FIG. 2b. 
For inside-casing gravel packing, washdown, reverse-circulation, and crossover methods are used as shown in FIGS. 3a, 3b, and 3c. In the washdown method, the gravel 22 is placed opposite the production interval 6 before the screen 16 is placed, and then the screen is washed down to its final position. The reverse-circulation and crossover methods are analogous to those used in open holes. Gravel 22 is first placed below the perforated interval 4 by circulation through a section of screen called the telltale screen 24. When this has been covered, the pressure increases, signaling the beginning of the squeeze stage. During squeezing, the carrier fluid leaks off to the formation, placing gravel in the perforation tunnels. After squeezing, the washpipe is raised, and the carrier fluid circulates through the production screen, filling the casing-production screen annulus with gravel. Gravel is also placed in a section of blank pipe above the screen to provide a supply of gravel as the gravel settles.
In deviated wells, gravel packing is greatly complicated by the fact that the gravel tends to settle to the low side of the hole, forming a dune in the casing-screen annulus. This problem is significant at deviations greater than 45xc2x0 from vertical. Gravel placement is improved in deviated wells by using a washpipe that is large relative to the screen because this causes a higher velocity over the dune in the annulus between the screen and the casing by increasing the resistance to flow in the screen-wash-pipe annulus.
Another form of sand control involves a tightly wrapped wire around a mandrel having apertures, wherein the spacing between the wraps is dimensioned to prevent the passage of sand. FIGS. 4 and 5 illustrate such a sand screen 10. The primary sand screen 10 is a prepacked assembly that includes a perforated tubular mandrel 38 of a predetermined length, for example, 20 feet. The tubular mandrel 38 is perforated by radial bore flow passages 40 that may follow parallel spiral paths along the length of the mandrel 38. The bore flow passages 40 provide for fluid through the mandrel 38 to the extent permitted by an external screen 42, the porous prepack body 58 and an internal screen 44, when utilized. The bore flow passages 40 may be arranged in any desired pattern and may vary in number in accordance with the area needed to accommodate the expected formation fluid flow through the production tubing 18.
The perforated mandrel 38 preferably is fitted with a threaded pin connection 46 at its opposite ends for threaded coupling with the polished nipple 34 and the production tubing 18. The outer wire screen 42 is attached onto the mandrel 38 at opposite end portions thereof by annular end welds 48. The outer screen 42 is a fluid-porous, particulate restricting member that is formed separately from the mandrel 38. The outer screen 42 has an outer screen wire 50 that is wrapped in multiple turns onto longitudinally extending outer ribs 52, preferably in a helical wrap. The turns of the outer screen wire 50 are longitudinally spaced apart from each other, thereby defining rectangular fluid flow apertures Z therebetween. The apertures Z are framed by the longitudinal ribs 52 and wire turns for conducting formation fluid flow while excluding sand and other unconsolidated formation material.
As shown in FIG. 5, the outer screen wire 50 is typically 90 mils wide by 140 mils tall in a generally trapezoidal cross-section. The maximum longitudinal spacing A between adjacent turns of the outer wire wrap is determined by the maximum diameter of the fines that are to be excluded. Typically, the aperture spacing A between adjacent wire turns is 20 mils.
The outer screen wire 50 and the outer ribs 52 are formed of stainless steel or other weldable material and are joined together by resistance welds W at each crossing point of the outer screen wire 50 onto the outer ribs 52 so that the outer screen 42 is a unitary assembly which is self-supporting prior to being mounted onto the mandrel 38. The outer ribs 52 are circumferentially spaced with respect to each other and have a predetermined diameter for establishing a prepack annulus 54 of an appropriate size for receiving the annular prepack body 58, described hereafter. The longitudinal ribs 52 serve as spacers between the inner prepack screen 44 and the outer screen 42. The fines which are initially produced following a gravel pack operation have a fairly small grain diameter, for example, 20-40 mesh sand. Accordingly, the spacing dimension A between adjacent turns of the outer screen wire 50 is selected to exclude sand fines that exceed 20 mesh.
Clearly, the design and installation of sand control technology is expensive. Yet, there is a drawback to all of the prior art discussed, namely the lack of feedback from the actual events at the formation face during completion and production. A need exists for the ability to detect conditions at the sand screen and convey that information reliably to the surface. Nothing in the prior art discloses a convenient way to provide for the passage of the conductors across a sand screen assembly. And yet were sensors to be placed inside and around the sand screen numerous benefits would be realized.
Sensors could be chosen that would provide real time data on the effectiveness of the sand placement operation. Discovering voids during the placement of the sand would allow the operator to correct this undesirable situation. Additionally, sensors could provide information on the fluid velocity through the screen, which is useful in determining the flow profile from the formation. Furthermore, sensors could provide data on the constituent content of oil, water and gas. All of these streams of information will enhance the operation of the production from the well.
The present invention relates to an improved sand screen, and, a method of detecting well conditions during sand placement and controls that allow modification of operational parameters. The sand screen includes at least one sensor directly coupled to the sand screen assembly and at least one actuator capable of affecting sand placement distribution, packing efficiency and controlling well fluid ingress. Each of the benefits described can be derived from the use of a sensor and actuator integrated into the sand screen.
A variety of sensors can be used to determine downhole conditions during the placement of the sand and later when produced fluids move through the screen into the production tubing string. This allows real time bottom hole temperature (BHT), bottom hole pressure (BHP), fluid gradient, velocity profile and fluid composition recordings to be made before the completion, during completion and during production with the production seal assembly in place. One particularly beneficial application for the use of sensors on the sand screen includes the measurement and recordation of the displacement efficiency of water based and oil based fluids during circulation. A user can also record alpha and beta wave displacement of sand. Sensors on the sand screen also allow measurement of after pack sand concentrations; as well as sand concentrations and sand flow rates during completion. Sensors also allow the determination of the open hole caliper while running in hole with the sand screen, which would be very useful in determining sand volumes prior to the placement of the sand. Sensors can allow the user to record fluid density to determine gas/oil/water ratios during production and with the provision for controlling/modifying the flow profiles additional economic benefits will result, which will be discussed in more detail below. Temperature sensors can identify areas of water entry during production. The use of sensors also allows the determination of changes in pressure drops that is useful in determining permeability, porosity and multi-skins during production. Sensor data can be used to actuate down hole motors for repositioning flow controls to modify the production profiles and enhance the economic value of the completion in real time.
Sensor data may be fed into microprocessors located either at or near the sensor or alternatively at the surface. The microprocessor determines an optimum flowing profile based on predetermined flow profiles and provides a control signal to an activator to change the flow profile for a particular section of sand screen. A simple embodiment of this is shown in FIG. 10. An electric motor could be energized, based on the control signal, and the motor could operate a compact downhole pump. As the pump displaces fluid into a piston chamber, the piston would be urged to a new position and the attached flow control would then modify the production profile of that portion of sand screen. Many alternative flow controls could also be operated in a similar fashion.
Furthermore, in general, most gravel pack assemblies, which includes the sand screen assembly, are run into the wellbore and spaced across a single zone to be gravel packed. If several zones are to be gravel packed within the same wellbore, then a separate gravel pack assembly must be run into the wellbore for each zone. Each trip into the wellbore requires more rig time with the attendant high operating cost related to time. Recent technology offers a gravel pack system, which allows the operator to run a gravel pack assembly that is spaced across multiple producing zones to be gravel packed. Each zone is separated and isolated from the other zones by a downhole packer assembly. This multi-zone gravel pack assembly is run into the wellbore as a single trip assembly which includes the improved sand screen with sensors and actuators.